1. Field of the Invention
The present invention relates to a secondary battery, and more particularly to a secondary battery having an improved electrolyte containment structure.
2. Discussion of Related Art
Secondary batteries are rechargeable as opposed to primary batteries which are not rechargeable. Secondary batteries are used in electronic devices such as cellular phones, laptop computers, and camcorders. Lithium secondary batteries have high energy density unit per weight and supply 3.6 V of power, three times greater than nickel-cadmium batteries or nickel-hydrogen batteries.
Lithium secondary batteries use lithium oxide as a cathode electrode active material and carbon materials as anode electrode active materials. Generally, lithium secondary batteries are classified as liquid electrolyte batteries (lithium ion batteries) and high molecule electrolyte batteries (lithium polymer batteries) depending on the type of electrolyte used. Also, lithium secondary batteries may also be classified by their housing, such as cylinder types, square types, and pouch types.
FIG. 1 shows a sectional view of a conventional square type secondary battery 10. As illustrated in FIG. 1, the secondary battery 10 includes a can 11 housing an electrode assembly 12, and a cap assembly 20 sealing the can 11.
The electrode assembly 12 includes a cathode electrode plate 13, a separator 14 and an anode electrode plate 15. A cathode electrode tap 16 and an anode electrode tap 17 protrude from the cathode electrode plate 13 and the anode electrode plate 15, respectively.
The cap assembly 20 includes a cap plate 21 coupled with the can 11, an anode terminal 23 insulated from the cap plate 21 by a gasket 22, an insulating plate 24 on an interior-facing surface of the cap plate 21, and a terminal plate 25 electrically connected to the anode terminal 23. The cathode electrode tap 16 is electrically connected to the cap plate 21 and the anode electrode tap 17 is electrically connected to the anode terminal 23 through the terminal plate 25. Additionally, an electrolyte injection hole 26 providing a path through which electrolyte may be injected into the can 11 is formed on the cap plate 21.
FIG. 2A shows an electrolyte injection hole before it has been sealed and FIG. 2B shows an electrolyte injection hole of FIG. 2A after it has been sealed. As illustrated in FIGS. 2A and 2B, the electrolyte injection hole 26 is formed in the cap plate 21 with a taper 28. An aluminum ball 27 is placed on the taper 28 to seal the electrolyte injection hole 26 after electrolyte has been injected into the can 11. The ball 27 is compressed into the electrolyte injection hole 26 by a pressure device such as a press 1. The ball 27 is welded by the laser welding to form a weld 29 and seal the electrolyte injection hole 26.
However, the configuration of the taper 28 is such that the ball 27 does not always precisely and entirely seal the electrolyte injection hole 26 when the ball is pressed into the hole. Accordingly, electrolyte may leak from the can as indicated by the arrows in FIG. 2B, causing sparking or a potential explosion hazard.